A liquid crystal display device employing a backlight unit and a liquid crystal panel has conventionally had a problem of in-plane luminance non-uniformity. The in-plane luminance non-uniformity is caused by, for example, (i) individual differences among light sources used in the backlight unit and/or (ii) in-plane transmittance (optical transmittance) non-uniformity of the liquid crystal panel.
As for the backlight unit, a backlight unit in which a plurality of LED light sources are arranged has been provided in recent years. What are particularly seen as problems in such a backlight unit are (i) individual differences in output luminance among LEDs and (ii), in a case where LEDs of colors R, G, and B are used, differences in output luminance among the LEDs due to variation in deterioration property among the LEDs of the respective colors.
In a case where area control of an LED backlight is carried out in a liquid crystal display device employing the LED backlight, cumulative light emitting time of an LED varies from light-emitting region to light-emitting region, and deterioration in degree of the LED accordingly varies from light-emitting region to light-emitting region. This ultimately causes the in-plane luminance non-uniformity.
Patent Literature 1 discloses, as a technique for addressing such problems, a liquid crystal display device. Specifically, according to the liquid crystal display device, (i) a photosensor for detecting a light emission luminance of each region where an LED is arranged so as to correct the in-plane luminance non-uniformity and (ii) a luminance detected by the photosensor is compared with a target value so that an output of the LED is corrected.
FIG. 9 is an explanatory view illustrating how the in-plane luminance non-uniformity occurs in a liquid crystal display device in which a conventional LED backlight is employed. (a) of FIG. 9 illustrates how the in-plane luminance non-uniformity occurs in the liquid crystal display device. (b) of FIG. 9 illustrates a state in which the in-plane luminance non-uniformity has been corrected in the liquid crystal display device.
As is clear from (a) of FIG. 9, an LED 101 in the middle is deteriorated and cannot output a luminance of 100, which is originally expected to be outputted by the LED 101 with 100% of its ability. The LED 101 is actually able to output a luminance of 80 instead of a luminance of 100. An LED 102 on the left and an LED 103 on the right, neither of which is deteriorated, are both able to output a luminance of 100 with 100% of their respective abilities. Since the luminance of the LED 101 in the middle is 80, a uniform in-plane luminance of 100 cannot be attained in a case where the liquid crystal panel has a transmittance of 100%. This causes the in-plane luminance non-uniformity.
In the state illustrated in (b) of FIG. 9, the luminance of the LED 102 on the left and the luminance of the LED 103 on the right are adjusted to a luminance of 80, which is a maximum luminance that can be outputted by the LED 101 in the middle which has been deteriorated. This allows each of the LEDs 101 through 103 to have a uniform luminance of 80, so that the in-plane luminance non-uniformity is corrected.
Patent Literature 2 discloses a method for making adjustment to non-uniformity of a luminance distribution on a surface of a liquid crystal panel in a liquid crystal display device in a case where a variation in brightness of a backlight causes the non-uniformity. Specifically, Patent Literature 2 discloses a method for correcting a video signal supplied to the liquid crystal display device so as to offset the non-uniformity in the luminance distribution on the surface of the liquid crystal panel.
Patent Literature 3 discloses a technique of carrying out area control of an LED backlight in a liquid crystal display device employing the LED backlight.
Specifically, Patent Literature 3 discloses an LED backlight in which a plurality of LEDs are arranged vertically and horizontally in a matrix manner and light emission of the plurality of LEDs can be controlled individually. Control is carried out in accordance with an input video so that (i) only a pixel region that needs illumination light is irradiated with the illumination light and (b) a pixel region that has been colored deep-black is not irradiated with illumination light. A drive signal that can attain an optimum display is supplied to the liquid crystal panel, in consideration of the control of the LED backlight. This brings about effects such as of (i) lowering power consumption, which is made possible by turning off an LED in a region where the LED is unnecessary and (ii) improving contrast, which is made possible by reduction in black level luminance.
FIG. 10 is a circuit configuration diagram illustrating a control system of a conventional liquid crystal display device in accordance with Patent Literature 3. The circuit configuration illustrated in FIG. 10 generates, on the basis of a supplied video signal Vs, (i) LED control data for controlling light emission from each region of the backlight panel 2 and (ii) liquid crystal control data for displaying an optimum video on a liquid crystal panel 1 in accordance with a luminance of the backlight panel 2.